Tunnel Projects
Caldecott Tunnel, Fourth Bore




The Caldecott Tunnel is located on SR-24, a primary corridor between Alameda and Contra Costa counties in Northern California. A fourth bore is being added to the existing three bore tunnels.

For the prelminary design phase, EMI developed a site exploration program targeted to provide adequate subsurface data for the EIR phase and prepared a Geotechnical Report.

For final design, EMI developed ground motion criteria and performed seismic response analyses for the tunnels and portal slopes. As the tunnel is located along the Caltrans’ lifeline route and lies within 1 kilometer from the Hayward Fault, the seismic design criteria were extremely stringent.

EMI performed probabilistic and deterministic seismic hazard evaluations using Next Generation Attenuation (NGA) models. Numerical analyses were performed to assess the earthquake-induced distortions and associated stresses in the new tunnel lining. Site-specific seismic coefficients were developed for use in pseudo-static analyses of tall retaining walls and cut slopes located outside of the tunnel portals. The design level peak ground acceleration (1.2g) and peak ground velocity (200 cm/s) were one of the most severe shaking conditions encountered by Caltrans.